Depends on how you're trained, I guess. With localized tension, you can grab the flat of a knife relatively easily (and with practice, know how/when to do it and stop doing it without thinking about it) and safely to apply physical and/or psychological leverage. It's﻿ all about context and how you do it...you don't want to fight for that knife, as "fighting for it" leads to tension, etc., but you do want to end up controlling it.

Depends,﻿ on your skill level, circumstances, a lot of things. Personally, and very generally, I think that a trained person should control the situation so that other less-trained people can go about their lives in safety and happiness.